Protesters in Hong Kong have been using Bluetooth mesh to communicate with one another so as to avoid using the Internet and therefore making it difficult for the Chinese authorities to intercept. However, this isn’t standard Bluetooth mesh as defined by the Bluetooth SIG. It’s a proprietary mesh protocol over standard Bluetooth.
The use of stand-alone Bluetooth mesh networks isn’t limited to protesters. A growing number of SDKs allow mesh networks to used by companies and organisations. When used with iOS and Android devices (which don’t necessary have to be smartphones) these provide for WiFi-less and Internet-less communication. This allows use, for example, in emergency situations when cellular and Internet goes down. Alternatively, they can simply provide connectivity across a site where there’s no cellular coverage or WiFi.